Energy efficient operation of radio network nodes and wireless communication devices in NB-IoT

ABSTRACT

A radio network node may operate in a normal or restricted operating state. In the restricted operating state, the radio network node may have just enough activity to enable UEs to detect the cell. The radio access node may transition to the normal operating state in response to messaging from a wireless communication device, such as reception of a random access preamble.

This application is a continuation of U.S. application Ser. No.16/081,570, filed Aug. 31, 2018, now U.S. Pat. No. 10,536,897, issuedJan. 14, 2020, which is a 371 of International Application No.PCT/IB2017/051206, filed Mar. 1, 2017, which claims benefit of U.S.Provisional Application No. 62/302,019, filed Mar. 1, 2016, thedisclosures of which are fully incorporated herein by reference.

TECHNICAL FIELD

The disclosed subject matter relates generally to telecommunications andmore particularly to an energy efficient radio base station for NB-IoT.

BACKGROUND

In recent years, energy efficiency has become an increasinglysignificant concern in many areas of commerce, includingtelecommunications. Energy efficiency has gained significance not onlyfrom an environmental point of view but also from an economical point ofview. For example, for mobile network operators, reducing powerconsumption results in less money spent on operating expenses.

3GPP has worked on this topic, resulting in several ideas that can bestudied, for example, in technical reports 3GPP TR 36.927 v. 13.0.0,entitled “Potential solutions for energy saving for E-UTRAN,” and TR36.887 v. 12.0.0, entitled “Study on energy saving enhancement forE-UTRAN”.

Certain approaches to reducing energy consumption in mobile networks arebuilt around overlapping cells where there is one or more so-calledcoverage cells which are always active and providing basic coverage andoverlapping so-called boost cells that may be switched on or off basedon network (NW) load generated by the user equipment (UE) in the cells.An example of this approach is illustrated in FIG. 1.

There are also solutions for non-overlapping cells, but these aredependent on having at least one coverage cell adjacent to thecompensation cells that may be switched on or off based on said load. Anexample of this approach is illustrated in FIG. 2.

In the scenarios shown in FIGS. 1 and 2, on/off switching of cells iscontrolled by the NW without specific UE interaction. This happenseither through a centralized operations-administration-maintenance (OAM)function based on e.g. load and traffic statistics obtained from thecells or via distributed/localized function based on informationexchange among adjacent cells.

Although the above approaches may be adequate where UEs are moving fromcoverage cells into boost/compensation cells (in which case the coveragecell can switch on the latter), there is no good way for a switched-offcell with no adjacent coverage cell to detect when UEs are switched onand in need of service.

SUMMARY

An object of embodiments herein is to facilitate energy efficientoperation of radio network nodes and wireless communication devices in awireless communications network implementing NB-IoT protocols.

According to a first aspect, there is presented a method of operating aradio network node. The method includes determining an operating stateof the radio network node. The method further includes selectivelytransmitting a restricted set of system information or a normal set ofsystem information according to the determined operating state.

In an embodiment according to the first aspect, the method furtherincludes detecting low-traffic network conditions, and, in response todetecting the low-traffic network conditions, transitioning from anormal operating state to a restricted operating state.

In another embodiment according to the first aspect, the methodincludes, during a restricted operating state, detecting a random accesspreamble transmitted by a wireless communication device, and, inresponse to detecting the random access preamble, transitioning from therestricted operating state to a normal operating state.

In any of the foregoing embodiments according to the first aspect, therestricted operating state is a low-power operating state.

In any of the foregoing embodiments according to the first aspect, themethod further comprises transmitting information indicating whether oneor more neighbor cells is in a restricted operating state.

According to a second aspect, there is presented a radio network nodecomprising at least one processor and memory containing instructionsthat, when executed by the at least one processor, cause the radionetwork node to perform embodiments of the method according to the firstaspect.

According to a third aspect, there is presented a method of operating awireless communication device. The method comprises detecting anoperating state of a radio network node. The method further comprises,in response to detecting that the operating state is a restrictedoperating state, transmitting information to the radio network node toinitiate a transition of the radio network node from the restrictedoperating state to a normal operating state.

In an embodiment according to the third aspect, the informationtransmitted to the radio network node comprises a random accesspreamble.

In any of the foregoing embodiments according to the third aspect,detecting the operating state of the radio network node comprisesdetecting a state indicator broadcast by the radio network node.

In any of the foregoing embodiments according to the third aspect, themethod further comprises receiving a restricted set of systeminformation from the radio access node during the restricted operatingstate, and receiving a normal set of system information from the radioaccess node during the normal operating state.

In any of the foregoing embodiments according to the third aspect,detecting the operating state of the radio network node comprises oneof: detecting the operating state based on information received in amaster information block (MIB); or detecting the operating state basedon synchronization signal patterns.

According to a fourth aspect, there is presented a wirelesscommunication device comprising at least one processor and memorycontaining instructions that, when executed by the at least oneprocessor, cause the wireless communication device to performembodiments of the method according to the third aspect.

According to a sixth aspect, there is presented a computer program foroperating a radio network node in an NB-IoT enabled system, the computerprogram comprising computer code which, when run on processing circuitryof the radio network node causes the radio network node to performembodiments of the method according to the first aspect.

According to a sixth aspect, there is presented a computer program foroperating a wireless communication device in an NB-IoT enabled system,the computer program comprising computer code which, when run onprocessing circuitry of the wireless communication device causes thewireless communication device to perform embodiments of the methodaccording to the third aspect.

Advantageously the disclosed methods, radio network nodes, wirelesscommunication devices, and computer programs allow for a radio networknode operating in an NB-IoT to conserve power, conserve networkbandwidth resources, and/or reduce network interference withoutcomprising a wireless communication device's ability to access thenetwork.

It is to be noted that any feature of the first, second, third, fourth,fifth, and sixth aspects may be applied to any other aspect, whereverappropriate. Likewise, any advantage of the first aspect may equallyapply to any of the other aspects, respectively, and vice versa. Otherobjectives, features and advantages of the enclosed embodiments will beapparent from the following detailed disclosure, from the attacheddependent claims as well as from the drawings. The steps of any methoddisclosed herein do not have to be performed in the exact orderdisclosed, unless explicitly stated.

BRIEF DESCRIPTION OF THE DRAWINGS

The drawings illustrate selected embodiments of the disclosed subjectmatter.

FIG. 1 illustrates two coverage cells providing basic coverage andoverlapping boost cells that may be switched on/off based on neededcapacity.

FIG. 2 illustrates a coverage cell adjacent to compensation cells thatmay be switched on/off based on needed capacity.

FIG. 3 illustrates an RBS power saving state where a RBS switches off atransmitter; during a switched-on period, a restricted set ofsignal/information is transmitted for UE to detect and camp on the cell.

FIG. 4 is a diagram illustrating an LTE network according to anembodiment of the disclosed subject matter.

FIG. 5 is a diagram illustrating a wireless communication deviceaccording to an embodiment of the disclosed subject matter.

FIG. 6 is a diagram illustrating a radio access node according to anembodiment of the disclosed subject matter.

FIGS. 7A and 7B are flowcharts illustrating a method of operating aradio access node according to an embodiment of the disclosed subjectmatter.

FIG. 8 is a diagram illustrating a radio access node according to anembodiment of the disclosed subject matter.

FIG. 9 is a flowchart illustrating a method of operating a wirelesscommunication device according to an embodiment of the disclosed subjectmatter.

FIG. 10 is a diagram illustrating a wireless communication deviceaccording to an embodiment of the disclosed subject matter.

FIG. 11 is a diagram illustrating a computer program product comprisingcomputer readable means according to an embodiment of the disclosedsubject matter.

DETAILED DESCRIPTION

The following description presents various embodiments of the disclosedsubject matter. These embodiments are presented as teaching examples andare not to be construed as limiting the scope of the disclosed subjectmatter. For example, certain details of the described embodiments may bemodified, omitted, or expanded upon without departing from the scope ofthe described subject matter.

Certain embodiments of the disclosed subject matter provide improvedenergy efficiency for an NB-IoT system, which is a narrowband (180 KHzbandwidth) system being developed for cellular internet of things by3GPP. The system is based on existing LTE systems and addressesoptimized network architecture and improved indoor coverage for massivenumber of devices with the following characteristics:

-   -   low throughput devices (e.g., about 2 Kbps)    -   low delay sensitivity (approximately 10 seconds)    -   ultra-low device cost (below 5 dollars)    -   low device power consumption (battery life of 10 years)

It is envisioned that each cell (covering approximately 1 squarekilometer) in this system will serve thousands (approximately 50thousand) wireless communication devices such as sensors, meters,actuators, and the like.

In certain embodiments, once a radio base station (RBS) (also referredto herein as a radio access node or radio network node) goes into powersaving state, only certain signaling/information essential for a UE todetect/measure the cell is still transmitted periodically. In-betweenthe periods, the RBS is switched off.

The UE entering the cell informs the RBS that service is needed and as aresult the RBS leaves the power saving state.

A potential benefit of this approach is that an RBS without anysupportive adjacent cell can save power and wake up to become fullyoperational exactly when needed by a UE entering the cell.

In an NB-IoT context, for a UE to be able to camp on a cell and acquireservice a set of procedures may comprise:

-   -   (initial) cell search to find and measure the quality of the        cell,    -   reading of broadcast information by the UE to see whether it is        allowed to camp on the cell and acquiring necessary information        for being able to access the cell, and    -   initiating a connection request through a random access        procedure.

For NB-IoT currently 3GPP standardization work is ongoing for definingthe details of how the foregoing set of procedures may be carried out.

For the cell search procedure it is in the present document assumed thatthe 3GPP standards for NB-IoT will, as in LTE, base the cell searchprocedure design on two synchronization signals: a PrimarySynchronization Signal (NB-PSS) and a Secondary Synchronization Signal(NB-SSS).

It is further assumed that from the NW broadcast information, the UE mayneed to at minimum read the Master Information Block (MIB) for derivingthe cell frame timing, the System Information Block 1 (SIB1) forderiving thresholds to see if the cell is suitable and also schedulinginformation about other SIBs that might be needed, and finally SIB2 forderiving the parameters necessary for accessing the cell.

The above assumptions may not hold true in certain circumstances, andother details may vary as well. For instance, the synchronizationsignals may be different and have different names, the broadcastinformation may be in other SIBs than those mentioned. Nevertheless,described concepts are still applicable in alternative scenarios, aswill be understood by those skilled in the art.

For the sake of simplicity, in the present document two different RBSstates are described. Note that the states below could apply either tothe complete bandwidth covered by the RBS or only parts of it (e.g. whenan NB-IoT in-band deployment is implemented where bandwidth/resourceblocks are shared between LTE and NB-IoT communications):

-   -   Fully-operational state (also referred to herein as a normal        operating state), in which the RBS receiver and transmitter are        available for providing full service to the UEs.    -   Power saving state (also referred to herein as a restricted        operating state) in which the RBS switches off the transmitter        and only switches it on periodically. During switched-on period,        a restricted set of system information is transmitted for UEs to        detect and camp on the cell. Similarly, the receiver may be        switched on periodically to detect potential access requests        from UEs.

FIG. 3 illustrates example behavior of an RBS operating in therestricted operating state and a nearby UE that is searching for aninitial cell for network access. The RBS switches on and off for certainperiods of time in the restricted operating state. The switch-on periodmay be shorter than the switch-off period, as depicted, or may be longerin certain embodiments. During the switch-on period a restricted set ofsystem information is transmitted for a UE to be able to detect and useto camp on the cell and acquire service.

The UE may begin a cell search during the switch-on period, as shown, orduring the switch-off period. If it begins the cell search during theswitch-on period the UE will be able to detect the system informationtransmitted during the switch-on period. The RBS switch-off period isshorter than a period in which the UE is configured to perform theinitial cell search to ensure that the initial cell search periodoverlaps with a switch-on period of the RBS.

Alternatively, the UE's initial cell search period is configured basedon a length of the RBS's switch-off period. For example, in oneembodiment the switch-off period is much longer than the switch-onperiod and much longer than a typical UE's initial cell search period.In such an embodiment, the UE may be configured with an initial cellsearch period that is longer than the expected RBS transmitterswitch-off period. Such a long initial cell search period may beacceptable in, for example, certain stationary UE applications.Moreover, the UE may be configured to learn the RBS transmitterswitch-off period (e.g., by observation or by explicit signalingreceived from the RBS) and may adapt its initial cell search period whensubsequently accessing the RBS. For example, if the RBS transmitterswitch-off period is 2 minutes and the UE initial cell search period is5 minutes, the UE may, upon learning the RBS transmitter switch-offperiod, reduce its initial cell search period to 2.5 minutes insubsequent access request procedures. In embodiments where one or moreUEs are configured with such adaptive behavior, the RBS switch-offperiod and the UE initial cell search period may be set anywhere fromabout 1 minute to about 10 minutes.

In one embodiment, the transmitter and receiver of the RBS are switchedon and off according to the same frequency. However, in otherembodiments, the transmitter may be switched off more frequently thanthe receiver to save more power and preserve more networkbandwidth/resources without compromising the ability of the RBS toreceive access requests from UEs and switch to the normal operatingstate.

More states may exist than the restricted operating state and the normaloperating state. For example, a fully dormant state may be entered,e.g., in case an adjacent coverage cell is available, or an OAM functioncompletely switches off the RBS during off-peak hours or the like.

In the power saving state, the RBS aims to only provide systeminformation that is necessary for a UE to camp on and access the cell,with examples of such system information including the followingsignals:

-   -   Synchronization signals NB-PSS and NB-SSS,    -   MIB on NB-PBCH,    -   SIB1 on NB-PDSCH,    -   SIB2 on NB-PDSCH

Note that although the same period is given for all signals as anexample in FIG. 3 for simplicity, the periodicity of each of the abovesignals may differ, e.g., SIB2 might be broadcasted much less often thanthe synchronization signals. Also, the above system information/signalsare transmitted far less often in the restricted operating state than inthe fully-operational state.

In the restricted operating state, the switch-off period in-between thetransmission of synchronization signals may be about 100 to about 800milliseconds since a UE typically searches cells on one carrierfrequency for a few seconds before switching to another frequency.

Also in this state, the RBS receiver is switched on periodically todetect NB-PRACH preambles. Upon such detection, the RBS changes state tothe fully-operational state. The receiver switch-on period and thespecific preamble to use by the UE for accessing the cell could eitherbe broadcast as part of the system information (e.g., SIB2) orpredefined in case the UE knows that the RBS is in the power savingstate. Thus based on the latter (predefined configuration), in someembodiments, SIB2 is not necessary to be broadcast and hence more powercan be saved as a result of less transmitter activity. Note thatdifferent preamble sequence configurations are needed to bepredefined/broadcast for UEs in different coverage levels.

There could be different ways for the UE to detect that the RBS isoperating in Power Saving state. In some embodiments an indicator couldbe introduced to be broadcasted e.g. in the MIB.

In some embodiments, the UE can detect the operating state based onsignal patterns, such as periodicity, of one or more synchronizationsignals, such as NB-PSS and/or NB-SSS.

In some embodiments, the aforementioned receive and/or transmitswitch-on and switch-off periods during the power saving state mightdiffer at different points in time, e.g. sparser during off-peak hoursand denser during other. Moreover, in certain embodiments the receiveswitch-off period may be held constant while the transmit switch-offperiods for at least some of the transmitted signals may be adaptivelylengthened based on traffic conditions to preserve power and networkresources. The receive switch-off period may be held constant (or belowan upper threshold), e.g., to ensure suitably low latency network accessfor UEs.

In some embodiments, cells can introduce and broadcast a state indicatorand schedule for neighboring cells to help out in the cell reselectionscenarios. The neighboring cell states and schedule could becommunicated among cells through the X2 interface or via a centralizedOAM function.

The described embodiments may be implemented in any appropriate type ofcommunication system supporting any suitable communication standards andusing any suitable components. As one example, certain embodiments maybe implemented in an LTE network, such as that illustrated in FIG. 4.

Referring to FIG. 4, a communication network 400 comprises a pluralityof wireless communication devices 405 (e.g., conventional UEs, machinetype communication [MTC]/machine-to-machine [M2M] UEs) and a pluralityof radio access nodes 410 (e.g., eNodeBs or other base stations).Communication network 400 is organized into cells 415, which areconnected to a core network 420 via corresponding to radio access nodes410. Radio access nodes 410 (also referred to herein as radio networknodes or radio base stations) are capable of communicating with wirelesscommunication devices 405 along with any additional elements suitable tosupport communication between wireless communication devices or betweena wireless communication device and another communication device (suchas a landline telephone).

Although wireless communication devices 405 may represent communicationdevices that include any suitable combination of hardware and/orsoftware, these wireless communication devices may, in certainembodiments, represent devices such as an example wireless communicationdevice illustrated in greater detail by FIG. 5. Similarly, although theillustrated radio access node may represent network nodes that includeany suitable combination of hardware and/or software, these nodes may,in particular embodiments, represent devices such as the example radioaccess node illustrated in greater detail by FIG. 6.

Referring to FIG. 5, a wireless communication device 500 comprises aprocessor 505, a memory, a transceiver 515, and an antenna 520. Incertain embodiments, some or all of the functionality described as beingprovided by UEs, MTC or M2M devices, and/or any other types of wirelesscommunication devices may be provided by the device processor executinginstructions stored on a computer-readable medium, such as the memoryshown in FIG. 5. Alternative embodiments may include additionalcomponents beyond those shown in FIG. 5 that may be responsible forproviding certain aspects of the device's functionality, including anyof the functionality described herein.

Referring to FIG. 6, a radio access node 600 comprises a node processor605, a memory 610, a network interface 615, a transceiver 620, and anantenna 625. In certain embodiments, some or all of the functionalitydescribed as being provided by a base station, a node B, an enodeB, agnodeB, and/or any other type of network node may be provided by nodeprocessor 605 executing instructions stored on a computer-readablemedium, such as memory 610 shown in FIG. 6. Alternative embodiments ofradio access node 600 may comprise additional components to provideadditional functionality, such as the functionality described hereinand/or related supporting functionality.

FIGS. 7A and 7B are flowcharts illustrating a method 700 of operating aradio access node according to an embodiment of the disclosed subjectmatter.

Referring to FIG. 7A, the method 700 comprises determining an operatingstate of the radio network node (S705), and selectively transmitting arestricted set of system information or a normal set of systeminformation according to the determined operating state (S710). During afully-operational state (e.g., a “normal operating state”), the radionetwork node may be available for providing full service to UEs. In apower saving state (e.g., a “restricted operating state”), the radionetwork node may switch off the transmitter and only switch it onperiodically. During switched-on period, the restricted set ofsignal/information may be transmitted for UEs to detect and camp on thecell. Similarly, the RBS receiver may be switched on periodically todetect potential access from the UE. For example, the RBS receiver maybe configured to receive a random access preamble from a wirelesscommunication device during the restricted operating state. In responseto detecting the random access preamble, the RBS transitions from therestricted operating state to a normal operating state.

Referring to FIG. 7B, the method may further include detectinglow-traffic network conditions (S715), in response to which the radionetwork node transitions from a normal operating state to a restrictedoperating state (S720). Moreover, while in the restricted operatingstate, the radio network node detects a random access preambletransmitted by a wireless communication device (S725) and, in responseto detecting the random access preamble, transitions from the restrictedoperating state to the normal operating state (S730).

The normal set of system information typically comprises, in addition tonecessary synchronization signals (which be sparse in time depending onthe operational state), a number of blocks. These blocks typicallyinclude, at a minimum, a Master Information Block (MIB), which containsa System Frame Number, LTE inband information, Access Barring indicator,SIB1 scheduling information, etc., a System Information Block (SIB1)containing PLMN Id, Tracking areas code, Cell selection parameters,scheduling information for other SIBs, an SIB2 containing Channelconfiguration for BCCH, PCCH and channels needed for accessing the cell.The above would typically constitute a minimum amount of SIBs that wouldbe needed for being operational in a cell, although other SIBs aretypically used as well, such as e.g. SIBs a 3, 4, 5 for neighbor cellinformation, SIB16 for UTC, etc.

The above-mentioned MIB/SIBs (MIB, SIB1, SIB2) are typically broadcastin the normal state. In contrast, in the restricted operating state(e.g., a power saving state), all channel configurations may not beneeded in SIB2 (only the random access preamble for accessing the cell).Alternatively, SIB2 may not need to be broadcast at all if, for example,a technical specification predefines a random access preamble forturning on a cell. In certain embodiments the MIB includes an indicatorthat tells the UE that it is operating in the power saving state andhence the UE knows that condensed versions of SIB1/2 are expected to bedecoded.

FIG. 8 is a diagram illustrating a radio access node 800 according to anembodiment of the disclosed subject matter. Referring to FIG. 8, theradio access node 800 comprises a determining module 805 configured todetermine an operating state of the radio network node, and atransmission module 810 configured to selectively transmit a restrictedset of system information or a normal set of system informationaccording to the determined operating state.

FIG. 9 is a flowchart illustrating a method 900 of operating a wirelesscommunication device according to an embodiment of the disclosed subjectmatter. Referring to FIG. 9, the method 900 comprises detecting anoperating state of a radio network node (S905), and in response todetecting that the operating state is a restricted operating state,transmitting information to the radio network node to initiate atransition of the radio network node from the restricted operating stateto a normal operating state (S910).

In one embodiment, the wireless communication device first receivessignals from the radio network node (S915) to be able to detect theoperating state. For example, the wireless communication device mayreceive a restricted set of system information from the radio accessnode during the restricted operating state, and receiving a normal setof system information from the radio access node during the normaloperating state. Based on which set of system information is received,the wireless communication device may detect the operating state of theradio network node. Alternatively, the wireless communication device maydetect the operation state by recognizing information received in amaster information block (MIB) as indicating that the radio network nodeis operating in the restricted operating state or based onsynchronization signal patterns.

FIG. 10 is a diagram illustrating a wireless communication device 1000according to an embodiment of the disclosed subject matter.

Referring to FIG. 10, the wireless communication device 1000 comprises adetection module 1005 configured to detect an operating state of a radionetwork node, and a transmission module 1010 configured to, in responseto detecting that the operating state is a restricted operating state,transmit information to the radio network node to initiate a transitionof the radio network node from the restricted operating state to anormal operating state.

In some embodiments, a computer program comprises instructions which,when executed by at least one processor, causes the at least oneprocessor to carry out the functionality of a radio access node (e.g.,radio access node 600 or 800) or another node (e.g., a remote processingnode that interfaces with the radio access node) implementing one ormore of the functions of the radio access node in a virtual environmentaccording to any of the embodiments described herein. Similarly, in someembodiments, a computer program comprises instructions which, whenexecuted by at least one processor, causes the at least one processor tocarry out the functionality of a wireless communication device (e.g.,wireless communication device 500 or 1000) according to any of theembodiments described herein.

FIG. 11 shows one example of a computer program product 1110 a, 1110 bcomprising computer readable means 1130. On this computer readable means1130, a computer program 1120 a can be stored, which computer program1120 a can cause the processing circuitry 210 and thereto operativelycoupled entities and devices, such as the communications interface 220and the storage medium 230, to execute methods according to embodimentsdescribed herein. The computer program 1120 a and/or computer programproduct 1110 a may thus provide means for performing any steps of the REas herein disclosed. On this computer readable means 1130, a computerprogram 1120 b can be stored, which computer program 1120 b can causethe processing circuitry 310 and thereto operatively coupled entitiesand devices, such as the communications interface 320 and the storagemedium 330, to execute methods according to embodiments describedherein. The computer program 1120 b and/or computer program product 1110b may thus provide means for performing any steps of the REC as hereindisclosed.

In the example of FIG. 11, the computer program product 1110 a, 1110 bis illustrated as an optical disc, such as a CD (compact disc) or a DVD(digital versatile disc) or a Blu-Ray disc. The computer program product1110 a, 1110 b could also be embodied as a memory, such as a randomaccess memory (RAM), a read-only memory (ROM), an erasable programmableread-only memory (EPROM), or an electrically erasable programmableread-only memory (EEPROM) and more particularly as a non-volatilestorage medium of a device in an external memory such as a USB(Universal Serial Bus) memory or a Flash memory, such as a compact Flashmemory. Thus, while the computer program 1120 a, 1120 b is hereschematically shown as a track on the depicted optical disk, thecomputer program 1120 a, 1120 b can be stored in any way which issuitable for the computer program product 1110 a, 1110 b.

As indicated by the foregoing, certain embodiments of the disclosedsubject matter relate to semi-operation of a radio base station (RBS)with just enough activity to enable UEs to detect the cell. The RBS maybecome fully operational with the help of UE through usage of a randomaccess preamble transmission.

The following abbreviations are used in this written description.

Abbreviation Explanation LTE Long Term Evolution MIB Master InformationBlock NB Narrowband NB-IoT NB Internet of Things NB-DLSCH NB DownlinkShared Channel NB-PRACH NB Physical Random Access Channel NB-PSS NBPrimary Synchronization Signal NB-SSS NB Secondary SynchronizationSignal NB-PBCH NB Physical Broadcast Channel NW Network OAM Operations,Administration, Maintenance RBS Radio Base Station SIB1 SystemInformation Block 1 SIB2 System Information Block 2 UE User Equipment

While the disclosed subject matter has been presented above withreference to various embodiments, it will be understood that variouschanges in form and details may be made to the described embodimentswithout departing from the overall scope of the disclosed subjectmatter.

The invention claimed is:
 1. A method of operating a wirelesscommunication device, comprising: receiving state indicator informationbroadcast by a radio network node, the state indicator informationindicating an operating state of a neighbor cell of the radio networknode, wherein the operating state of the neighbor cell comprises anormal operating state in which the neighbor cell transmitssynchronization signals according to a first periodicity and arestricted operating state in which the neighbor cell transmits thesynchronization signals according to a second periodicity; adapting acell search period based on the state indicator information, and furtherbased on a transmit switch-on period and a transmit switch-off period ofthe neighbor cell, wherein the transmit switch-on period is a period oftime during which a transmitter of the neighbor cell is periodicallyswitched on to transmit the synchronization signals when the neighborcell is in the restricted operating state, wherein the transmitswitch-off period is a period of time during which the transmitter ofthe neighbor cell is periodically switched off to save power when theneighbor cell is in the restricted operating state; and receiving thesynchronization signals from the neighbor cell during the adapted cellsearch period.
 2. The method of claim 1, wherein the state indicatorinformation includes information about a periodicity of thesynchronization signals received from the neighbor cell.
 3. The methodof claim 1, further comprising: receiving a restricted set of systeminformation from the neighbor cell during the restricted operatingstate, and receiving a normal set of system information from theneighbor cell during the normal operating state.
 4. The method of claim1, further comprising: detecting the operating state based oninformation received in a master information block (MIB); or detectingthe operating state based on synchronization signal patterns.
 5. Awireless communication device, comprising: at least one processor; andat least one memory containing instructions that, when executed by theat least one processor, cause the wireless communication device to:receive state indicator information broadcast by a radio network node,the state indicator information indicating an operating state of aneighbor cell of the radio network node, wherein the operating state ofthe neighbor cell comprises a normal operating state in which theneighbor cell transmits synchronization signals according to a firstperiodicity and a restricted operating state in which the neighbor celltransmits the synchronization signals according to a second periodicity;adapt a cell search period based on the state indicator information, andfurther based on a transmit switch-on period and a transmit switch-offperiod of the neighbor cell, wherein the transmit switch-on period is aperiod of time during which a transmitter of the neighbor cell isperiodically switched on to transmit the synchronization signals whenthe neighbor cell is in the restricted operating state, wherein thetransmit switch-off period is a period of time during which thetransmitter of the neighbor cell is periodically switched off to savepower when the neighbor cell is in the restricted operating state; andreceive the synchronization signals from the neighbor cell during theadapted cell search period.
 6. The wireless communication device ofclaim 5, wherein the state indicator information includes informationabout a periodicity of the synchronization signals received from theneighbor cell.
 7. The wireless communication device of claim 5, whereinthe at least one processor and memory are further configured to causethe wireless communication device to receive a restricted set of systeminformation from the neighbor cell during the restricted operatingstate, and receive a normal set of system information from the neighborcell during the normal operating state.
 8. A non-transitorycomputer-readable media having stored thereon a computer program foroperating a wireless communication device in an NB-IoT enabled system,the computer program comprising computer code which, when run onprocessing circuitry of the wireless communication device causes thewireless communication device to: receive state indicator informationbroadcast by a radio network node, the state indicator informationindicating an operating state of a neighbor cell of the radio networknode, wherein the operating state of the neighbor cell comprises anormal operating state in which the neighbor cell transmitssynchronization signals according to a first periodicity and arestricted operating state in which the neighbor cell transmits thesynchronization signals according to a second periodicity; adapt a cellsearch period based on the state indicator information, and furtherbased on a transmit switch-on period and a transmit switch-off period ofthe neighbor cell, wherein the transmit switch-on period is a period oftime during which a transmitter of the neighbor cell is periodicallyswitched on to transmit the synchronization signals when the neighborcell is in the restricted operating state, wherein the transmitswitch-off period is a period of time during which the transmitter ofthe neighbor cell is periodically switched off to save power when theneighbor cell is in the restricted operating state; and receive thesynchronization signals from the neighbor cell during the adapted cellsearch period.
 9. The non-transitory computer-readable media of claim 8,wherein the state indicator information includes information about aperiodicity of the synchronization signals received from the neighborcell.
 10. The non-transitory computer-readable media of claim 8, whereinthe computer program is further configured to cause the wirelesscommunication device to receive a restricted set of system informationfrom the neighbor cell during the restricted operating state, andreceive a normal set of system information from the neighbor cell duringthe normal operating state.